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Re: NEW BRIDGE[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: NEW BRIDGE
- From: Steve Gordin <sgordin(--nospam--at)sgeconsulting.com>
- Date: Sat, 22 May 2010 08:04:44 -0700
The Tacoma Narrows bridge spanned
335-853-335 meters, and was a unique - not to say daring - structure,
even for that age of daring structures. The Gallopin' Gertie had quite extreme characteristic ratios: width-to-span 1/72 (1/47 for
Golden Gate bridge), depth-to-span -1/350 vs. a "conventional" 1/30. |
At the time, the third-party review had warned about the potential danger of such design, but was essentially self-muffed, apparently, due to the authority of the bridge designer (famous suspension bridge engineer Leon Moiseiff). The Tacoma Narrows Bridge "galloped" from the time of construction, nauseating the workers; it collapsed less than 6 months after opening under a 40MPH wind.
The subsequent investigation resulted in wider development of the wind-tunnel testing, which helped to recognize flutter and inadequate torsional stiffness as the main causes of collapse. Ever since then, the cross-sections of the long-span bridges were aerodynamically shaped and/or very rigid.
The bridge in Volgograd was built 70 years after Tacoma, and is nothing unique (may be, except for its price tag), with girders spanning 150m and considerable width and depth. If I understand correctly, the wind at the time of the incident was about 14 m/sec (31MPH). The mode of oscillations is quite similar to Tacoma, and seems to look like flutter.
I already asked, and hope to get an answer from, one of the leading vibration experts regarding that phenomenon. I also hope that, for the sake of all bridge designers and the safety of the general public, the impending investigation of this bridge will be more transparent and less politicized that those of other recent structural failures in Russia.
Steve Gordin SE
- Re: NEW BRIDGE
- From: Alexander Bausk
- Re: NEW BRIDGE
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